Proposed Testing and Research Approach for Pyrrhotite-Induced … · Pyrrhotite-Induced Concrete...

US Army Corps of Engineers Engineer Research and Development Center

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UNCLASSIFIED DISCOVER | DEVELOP | DELIVER

Mr. Christopher M. Moore, Mr. Cody M. Strack, Dr. Robert D. Moser, Dr.

Gordon W. McMahon, Engineer Research and Development Center (ERDC)

US Army Corps of Engineers (USACE)

19 October 2018

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Proposed Testing and Research Approach for

Pyrrhotite-Induced Concrete Deterioration

Distribution A: Approved for public release


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This briefing presents recommendations for

test methods and approaches for

addressing pyrrhotite-induced expansion in

concrete. There is no standard procedure to

apply or guidance available. Almost all of

the recommendations require R&D ranging

from months to years to develop a solution.


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Phased approach

• Approach focused on addressing near-term regulatory needs and developing

approaches to identify, prioritize, and manage structures susceptible to concrete

damage from pyrrhotite-induced expansion.

• Quarry oversight / putting a “clamp” on deleterious aggregates • 1st phase conservative guidance based on chemistry

• 2nd phase to consider both mineralogy and chemistry – needs short term R&D

• Forensics on existing homes • Near-term recommendations for improving petrographic analysis

• Med-term improved analysis methods – needs med term R&D

• Projection of future damage – long term (5+ years) R&D needed

• Develop mitigation options – long term (1-3 years) R&D needed

• Best practices for concrete replacement - med term (1 year) R&D needed

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Aggregate Acceptance Based on Chemistry

Develop Fe-S Mineral Analysis

Method(s)


and Mineralogy

Use Petrography Methods and Standardize Reporting of Field Conditions and Analysis Results

Develop New Petrography / Forensic Analysis Methods: Chemistry, Mineralogy, Magnetic

Revised Approach for Field Assessment and

Forensic Analysis

R&D on Service Life Modeling Approaches

R&D on Mitigation Options: Environmental, Repair/Retrofit

R&D / Tradespace on Approaches for Replacement

Inform Approaches for Managing Existing Homes,

and Prioritizing Mitigation, Repair, and Replacement Activities

Immediate Near-Term Mid-Term Long-Term

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Quarry oversight

• Regulations on quarries for minimum

testing and acceptance requirements for

supply of aggregate materials to concrete

production industry

• Lean on testing standards from ASTM,

AASHTO currently used for aggregates,

cements, etc.

• Reference acceptance / rejection

requirements (i.e., limits on test results)

from Canadian and European Standards

• Frequency of testing based on quantity of

material that adjusts based on observed

variation in results

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Quarry Oversight


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Quarry oversight – basic requirements

• Aggregate must meet minimum

requirements of ASTM C33 Standard

Specification for Concrete Aggregates

• Gradations

• Deleterious Materials

• This requirement should already be in

place for materials to be used in

certified ready-mix concrete plant

• Does not cover chemical and

mineralogical concerns with pyrrhotite

in aggregate

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Quarry oversight – basic requirements

• No general standards that cover specifics

of chemical and mineralogical analysis of

aggregate

• Specific test method to identify pyrrhotite

at relevant resolution (e.g., 0.2-0.3%)

needs to be developed and vetted.

• Suggest immediate conservative focus

that assumes pyrrhotite is present and

uses standard test methods for chemical

analysis to qualify and aggregate for use

in concrete.

• 2nd phase would include mineral ID rather

than conservative focus on pyrrhotite.

• Recommend using specific standards /

test methods for chemistry and

mineralogy.

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Quarry Oversight – 1st phase sulfur content by XRF or

IR combustion • Leco infrared combustion sulfur analysis

• Obtain elemental sulfur (S) content

• X-ray fluorescence (XRF) measurements

on aggregate to identify bulk chemical

composition

• Performed on fused glass samples

following procedures in AASHTO M85

for cement

►Pulverize aggregate to produce

fused glass sample

–Pulverize sample to 90% by mass

passing #325 (45 μm) sieve

• Obtain bulk chemistry using XRF

• Quantify elemental sulfur (S) content

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SiO2, % 20.0

Al2O3, % 5.0

Fe2O3, % 3.1

CaO, % 63.0

MgO, % 2.9

SO3, % 3.3

LOI, % 1.74

Na2O, % 0.15

K2O, % 0.5

TiO2, % 0.25

P2O5, % 0.05

C3A, % 8

C3S, % 67

C2S, % 6

C4AF, % 9


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Quarry Oversight – 1st phase accept / reject limits

for aggregate • Assume that pyrrhotite is present in

aggregate

• Accept aggregate if sulfur (S) content

<0.1%

• Otherwise, reject aggregate for use in

concrete

• Suggest that CT State Geologist has

input on this and if it is possible to just

apply this analysis regionally. However,

pyrrhotite geological maps are for non-

trace compositions. Relevant amounts of

pyrrhotite likely extend far beyond

mapped regions.

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Geological Map of

Connecticut


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Quarry Oversight – 1st phase qualification of laboratories

• Certification programs for laboratories to

conduct this testing are recommended:

• AASHTO Accredited

• ISO 17025

• Participate in Cement and Concrete

Reference Laboratory (CCRL) testing

proficiency sample program.

• Sulfur (S) content measurements are less

than typically present in cement. New low

S content calibrations will need to be

performed by laboratories to calibrate /

verify instruments.

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Quarry Oversight – 1st phase frequency of testing

• Recommend testing for every 25k tons or 3

months, whichever is most frequent

• Based on making testing less than 1% of

operating cost

• Assumed testing cost $5k and rock price

$25/ton

• Perform this testing four times

• If variability in results is less than +/-10% of

mean of four test results, switch to

conducting once per year

• If higher variability observed, continue at

testing frequency specified above

• NOTE: CT State Geologist should have input

on this. The frequency / weight for each

interval of testing should be based on the

strata / heterogeneity in the formation.

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Becker’s Quarry, Willington CT


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Quarry oversight – 2nd phase mineralogy +

sulfur content

• A 2nd phase of implementation to also consider

mineralogy to understand Fe-S mineral present

• Fe-S mineral identification would guide selection of

acceptable limits on sulfur content

• Recommend optionally using either thin section

petrography by ASTM C295 or X-ray diffraction (or

other undiscovered) to qualitatively identify Fe-S

minerals

• Recommend using specific standards / test methods

for chemistry and mineralogy.

• Recommend a quality materials consultant /

laboratory services laboratory perform short-term

research to develop method rather than university.

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Quarry Oversight – 2nd phase X-ray diffraction for mineral ID

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• X-ray diffraction (XRD) measurements on aggregate to identify deleterious

minerals

• No specific procedures to apply. Can lean on ASTM C1365 and D934

• Example recommended operating procedures

• Pulverize sample to 90% by mass passing #325 (45 μm) sieve

• Random powder pack sample preparation

• Scan resolution of <0.1° 2θ

• Scan speed to achieve >10k counts on 100% peak

► Modern XRDs can do this with a 2hr scan / 0.67 °/min

• Scan between 20-100° 2θ

► Applicable to Cu and Co K-α sources

► Scan correlated to d-space between approx. 1-5 Å

• Identify if pyrrhotite and/or pyrite are present

► Using ICDD verified powder diffraction reference patterns

► If no pyrrhotite or pyrite is detected, no additional testing (i.e., XRF) is required

• Recommend a short study by quality analysis laboratory to run through

method and “tweak” any parameters


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Quarry Oversight – 2nd phase X-ray diffraction for

mineral ID

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Quarry Oversight – 2nd phase sulfur content by XRF or

IR combustion

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• Leco infrared combustion sulfur analysis

• Obtain elemental sulfur (S) content

X-ray fluorescence (XRF) measurements on

aggregate to identify bulk chemical composition

• Performed on fused glass samples

following procedures in AASHTO M85 for

cement ► Pulverize aggregate to produce fused glass sample

– Pulverize sample to 90% by mass passing #325

(45 μm) sieve

• Obtain bulk chemistry using XRF

• Quantify elemental sulfur (S) content


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Quarry Oversight – 2nd phase Accept / reject limits

for aggregate

• If pyrrhotite is observed by XRD and/or ASTM C295

• Accept aggregate if sulfur (S) content <0.1%

• Otherwise, reject aggregate for use in concrete

• If pyrrhotite is not observed but other Fe-S minerals are (e.g., pyrite) by XRD and/or

ASTM C295

• Accept aggregate if XRF sulfur (S) content <1%

• Otherwise, reject aggregate for use in concrete

• If no Fe-S minerals (i.e., pyrrhotite, pyrite) are observed by XRD and/or ASTM C295, no

objection to acceptance based on chemistry and mineralogy

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NOTE: Other methods for mineralogy and chemistry may be

available such as examination of magnetic properties.


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Quarry Oversight – 2nd phase qualification of laboratories

for testing • Certification programs for laboratories to

conduct this testing are recommended:

• AASHTO Accredited

• ISO 17025

• Participate in Cement and Concrete

Reference Laboratory (CCRL) testing

proficiency sample program.

• Sulfur (S) content measurements are less

than typically present in cement. New low S

content calibrations will need to be

performed by laboratories to calibrate /

verify instruments.

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Quarry Oversight – 2nd phase frequency of testing

• Recommend testing for every 25k tons or 3 months, whichever is most frequent

• Based on making testing less than 1% of operating cost

• Assumed testing cost $5k and local rock price $25/ton

• Perform this testing four times • If variability in results (max vs. min) <10%,

switch to conducting once per year

• If higher variability observed, continue at testing frequency specified above

• NOTE: CT State Geologist should have input on this. The frequency / weight for each interval of testing should be based on the strata

Stony Creek Quarry – Branford, CT


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Forensics – Using current procedures ASTM C856

• Currently ASTM C856 Standard Practice

for Petrographic Examination of

Hardened Concrete

• Need to standardize sample collection

• Sample from consistent location (i.e.,

basement wall with maximum soil

elevation)

• Report site conditions: water table,

waterproofing systems, sump present,

dehumidifier, HVAC in basement

• Report environmental conditions: internal

temperature and relative humidity in

basement

• Report damage: standard “classes” of

damage with visual rating guidance, note

efflorescence, etc.

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Forensics – Using current procedures ASTM C856

(cont’d) • Need to standardize reporting:

• Note presence of Fe-S minerals: pyrrhotite, pyrite, or

others

• Note if present in coarse and/or fine aggregate

• Note any other relevant features: SCMs used, rough

estimate of water-to-cement ratio, large voids and air

entrainment observations

• Provide semi-quantitative estimate of composition.

Below is an example potential binning:

► <0.1% / minor

► 0.1%-1% moderate

► 1%-10% high

► >10% very high

► Can base off of visual estimators applied to thin sections

► The resolution in these bins is difficult to obtain w/ current

analytical methods

• Would require some short term trials with concrete

from affected structures to refine method.

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Forensics – New method development, med term R&D

needed

• Full concrete petrography by ASTM C856 is

expensive and low resolution

• Need better method with high resolution to

quantify Fe-S content in existing concrete

• Ideally coring would not be required

• Many potential options:

• On-site forensic analysis using handheld instruments

• Collection of powders for laboratory-based analysis

• Improved petrographic analysis procedures to apply

to cores to improve resolution and speed of analysis

• Would recommend medium term R&D conducted

by quality materials consultant with expertise in

concrete materials, petrography, and unique test

methods

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Service Life Prediction for Infrastructure

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Projecting future concrete deterioration, long term

R&D needed

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• To project how concrete damage will occur in

future

• Map space of material, construction, exposure:

• Different pyrrhotite contents, coarse and/or fine

aggregate

• Different construction / basement types

• Different environments: water table, RH, etc.

• Laboratory testing:

• Simulate different variables with accelerated

laboratory-based expansion testing

• Goal would be to correlate observations from

forensic analysis and “bins” structure types to

project future damage

• Minimal expansion capacity, moderate, high,

very-high, etc.


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Develop potential mitigation options, long term

R&D needed

• Focus on R&D to understand if there’s anything that can be done to help mitigate expansion • French drains, upstream waterproofing,

dehumidifiers, or other (more outside-the-box) ways

• Results from the service life modeling research would provide information to guide potential mitigation options

• Would be tied to “bins” • 1: Minimal damage anticipated, no mitigation

needed

• 2: Mitigation can actually help to extend life of concrete

• 3: Nothing you can do – full replacement needed

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Best practices for full concrete replacement, med term

R&D needed

• Need to generate some best practices for

remediation / replacement of basements • Engineered solutions for typical basements

• Jack up house vs. wall-by-wall replacement

• Other innovative construction approaches

• In future, this guidance would roll into the

high risk “bin” for structures where full

replacement is needed

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Develop Fe-S Mineral Analysis

Method(s)


and Mineralogy

Use Petrography Methods and Standardize Reporting of Field Conditions and Analysis Results

Develop New Petrography / Forensic Analysis Methods: Chemistry, Mineralogy, Magnetic

Revised Approach for Field Assessment and

Forensic Analysis

R&D on Service Life Modeling Approaches

R&D on Mitigation Options: Environmental, Repair/Retrofit

R&D / Tradespace on Approaches for Replacement

Inform Approaches for Managing Existing Homes,

and Prioritizing Mitigation, Repair, and Replacement Activities

Immediate Near-Term Mid-Term Long-Term

IMPLEMENT

IMPLEMENT

IMPLEMENT

Agg

rega

te

Reg

ula

tio

ns

Stru

ctu

re

Ass

ess

men

t M

anag

emen

t an

d S

olu

tio

ns

Year 1-2 Year 3-4 Year 5-7 Year 8+

Proposed Testing and Research Approach for Pyrrhotite-Induced … · Pyrrhotite-Induced Concrete...

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